In recent years, the signal band of information communication devices such as PHS or portable telephones and the CPU clock time of computers reach to a GHz band and higher frequencies are coming to be used. The dielectric loss of electric signals is proportional to the product of the square root of dielectric constant of an insulator forming a circuit, the dielectric loss tangent thereof and the frequency of signals to be used. Therefore, as the frequency of signals to be used becomes higher, the dielectric loss increases. The dielectric loss damps electrical signals and impairs the reliability of the signals. For inhibiting the above impairment, it is required to select a material having a small dielectric constant and a small dielectric loss tangent as an insulator. As such a material, a fluorine-contained resin, a polyolefin resin, a polystyrene resin, a polyphenylene ether resin, etc., are proposed. However, although these resins are excellent in low dielectric characteristics, most of them have a problem about chemical resistance or moldability. With regard to films made of these resins for electrical insulating materials, for example, a film made of polyphenylene ether have a problem about flexibility (for example, JP-A-7-188362), and a film made of a low molecular weight styrene compound such as divinylbenzene is apt to have tackiness and a cured product obtained is apt to be fragile (for example JP-A-2002-249531). Further, the present inventors have developed vinyl compound derivatives of bifunctional polyphenylene ether oligomers for meeting a demand for low dielectric characteristics (for example, JP-A-2004-059644). These derivatives are excellent in low dielectric characteristics. However, when films are obtained from these derivatives, a crack is apt to occur. Therefore, an improvement is required.